1. Field of the Invention
The present invention relates to a dielectric device such as a dielectric filter or a duplexer and an electronic device using the same.
2. Description of the Related Art
Such dielectric devices are used in a high-frequency range such as sub-microwave band, microwave band, millimeter wave band, or sub-millimeter wave band. More specific examples of applications include satellite communication devices, mobile communication devices, wireless communication devices, high-frequency communication devices, or base stations for such communication devices.
Conventionally, resonators and dielectric filters used in portable phones and the like have been constructed by combining a plurality of resonating units each formed by providing one through-hole in a dielectric substrate, wherein the resonator length is generally determined by dividing a quarter of a wavelength λ of a free space by the square root of a relative dielectric constant of a material constituting the dielectric substrate.
Such a dielectric filter may be constructed by either connecting a plurality of resonators through a separately prepared coupling circuit or providing a generally rectangular parallelepiped-shaped dielectric substrate with a plurality of through-holes extending from one side to the opposite side, wherein the through-holes are fashioned into resonating units by metalizing five external surfaces of the dielectric substrate and inner walls of the through-holes.
In the case of using a dielectric substrate for the dielectric filter, an additional component may be added by providing an additional element such as a capacitor to the resonating unit or forming a conductive pattern on the non-metalized external surface. Furthermore, a groove or recess may be formed in the dielectric substrate itself to intentionally upset the balance of electromagnetic coupling distribution for achieving electric field or magnetic field coupling.
Each of the resonator units may be provided with first and second terminals, which may serve as input/output terminals. Typically, the first and second terminals are disposed on a surface intended to face a circuit board.
When the dielectric device is mounted with the first and second terminals facing the circuit board, however, although most of an external conductor film connects with an earthing conductor on the circuit board through a solder or the like, electrical coupling between the earthing conductor and an intermediate conductor film, which is a part of the external conductor film, shifts an attenuation pole, resulting in fluctuation of pass band width and other filter characteristics.
As an effective means to solve the problems of miniaturization and height reduction, Japanese Patent No. 3329450 discloses a novel dielectric device whose resonator unit is composed of a first hole and a second hole meeting one end of the first hole. However, this prior art document also fails to disclose a means to solve the above problems.